Conventionally, a brushless motor device is used as a driving source for driving an actuator for exhaust gas control, such as an EGR (Exhaust Gas Recirculation: exhaust gas recirculation) valve used for, for example, a vehicle, and a VG (Variable Geometvic) turbo actuator. This brushless motor device is provided with, for example, a stator whose slot number is “9”, a rotor whose pole number is “8”, a magnet for magnetic pole position detection whose pole number is 8 which is the same as that of the rotor, and three Hall ICs (ICs in each of which a Hall element is incorporated) for detecting the rotational position of the rotor by detecting the magnetism of this magnet for magnetic pole position detection. Such the brushless motor device in which the number of poles of the rotor is the same as that of the magnet for magnetic pole position detection and the three Hall ICs are included is referred to as a “single-precision brushless motor device” in this specification.
In recent years, a brushless motor device having a magnet for magnetic pole position detection whose pole number is increased up to “16” which is twice as many as the conventional number of poles in order to improve the resolution of detection of the rotational position of the rotor has been developed (for example, refer to patent reference 1). Such the brushless motor device in which the number of poles of the rotor is twice as many as that of the magnet for magnetic pole position detection and three Hall ICs are included is referred to as a “double-precision brushless motor device” in this specification. This double-precision brushless motor device can improve its resolution of detection of the rotational position of the rotor to twice as high as that of the single-precision brushless motor device.    [Patent reference 1] JP, 2002-252958, A
By the way, although the double-precision brushless motor device disclosed by above-mentioned patent reference 1 can detect the rotational position of the rotor with a fixed resolution, development of a brushless motor device which can detect the rotational position of a rotor with a finer resolution has been desired for, for example, an actuator for exhaust gas control and so on.
The present invention is made in order to meet the above-mentioned request, and it is therefore an object of the present invention is to provide a brushless motor device that can improve the resolution of detection of the rotational position of a rotor.